Hydraulic apparatus



Aug. 26, 1952 E. H. BORN 2,603,159

HYDRAULIC APPARATUS Filed Feb. 2, 1945 2 swans-4mm 1 IN V EN TOR.

Elli/s H'Born T ORNEY Aug. 26, 1952 E. H. BORN 2,603,159

HYDRAULIC APPARATUS Filed Feb. 2, 1945 2 SHEETSSHEET 2 FIG. 5

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' INVENTOR.

Ellis ELBorn BY ATTOFNEY Patented Aug. 26, 1952 HYDRAULIC APPARATUS Ellis H. Born, Bexley, Ohio, assignor to The Denison Engineering Company, Columbus, Ohio, a

corporation of Ohio Application February 2, 1945, Serial No. 575,864

1 13 Claims.

This invention relates generally to hydraulic mechanism and is particularly directed to a fluid pressure energy translating device which is capable of use either as a pump or a motor.

An object of this invention is to provide a fluid pump or motor of the axial piston type having a tilted swash or cam plate and bearing shoes between the pistons and the cam plate, the bearing shoes serving to distribute the force transmitted to the piston by the fluid in the cylinders, .over a greater area of the cam plate whereby wear will be decreased while the efficiency of the device is increased.

A further object of the invention is to provide an axial piston pump or motor having bearing shoes between the pistons and a cam plate and providing a recess in the surface of the shoe engaging the cam plate which recess will be in communication with the piston chamber through passages in the shoe and piston whereby the reaction of the fluid on the piston during the pressure stroke will be at least partially offset by the pressure of the fluid in the recess which fluid acts against the shoe and cam plate and tends to separate them.

A still further object of the invention is to pro- .vide the bearing shoes, mentioned above, with auxiliary bearing surfaces which are not subject to theaction of the fluid pressure'tending to separate the shoes and cam plate but merely increase the area over which the difference between the forces tending to' move the shoes toward and away from the cam plate may be distributed.

Another object consists in providing bearing shoes .of particular construction which will increase the efliciency of the device and minimize wear by preventing certain motions which would otherwise occur.

An object of the invention also is to provide a pump or motor of the axial piston variety with bearing shoes between the pistons and a cam plate, and part of the shoe in engagement with the cam plate being shaped like a sector of a ring and of such size that when the device is assembled with the shoes in engagement with the cam plate, adjacent shoes will prevent rotation of one another about the axis of the connection thereof with their respective pistons whereby wear or other undesirable result incident to such motion will be eliminated.

It is another object to provide an axial piston pump having bearing shoes between the piston ends and the cam plate, which members are so formed and connected that the forces tending to urge the pistons toward the cam plate will be counterbalanced by fluid pressure, means being provided to resiliently urge the bearing shoes toward the cam plate and mechanically resist separation thereof.

An object is to provide bearing shoes which have interlocking edges which cooperate with one another to prevent the rotative action of the shoes mentioned in a preceding paragraph.

In the construction of an axial piston pump it has been found desirable to utilize the fluid pressures generated in the pump to balance the forces tending to move the cylinder barrel away from the port plate and yet minimize the effects of such forces so that a sealing engagement between the cylinder barrel and port plate will always be maintained. It is also desirable to counterbalance the reaction of the fluid pressure which is transmitted through the pistons to the cam plate whereby the efficiency and life of the device will be increased. In previous devices of this character uneven wear has occurred due to the following causes: first, that greater pressure is developed on one side of the axis of rotation than on the other, second, that the force employed to counterbalance the reaction of the fluid on the pistons is not applied in a truly axial direction and third, that by reason of the inclination of the camplate there is a strong tendency to force the cylinder barrel to one side thus decreasing the effectiveness of the seal at the port plate end. It is, therefore, an object of the invention to provide improved bearing means for the cylinder barrel of the device which will tend to eliminate uneven wear by supporting the cylinder barrel at the most advantageous place.

In axial piston pumps and motors of the type mentioned, forces exist which tend to move the pistons toward the cam plate at all times, such forces being due to the pressure on the fluid in the piston chambers. These forces are counteracted by oppositely directed forces imparted by the cam plate to the pistons through the bearing shoes. These forces meet at points disposed in a plane passing through the centers of the ball and socket connections between the pistons and bearing shoes and cause resultant forces which tend to move the pistons in a lateral direction. These resultant forces, if not overcome in some way, will swing the cylinder barrel toward one side and move the bearing surface at the end thereof away from the valve plate thus permitting the escape of fluid under pressure and a resultant lowering in efliciency of the device. It is an object of this invention to provide the casing with a bearing for the cylinder barrel which bearing will be located most auspiciously to compensate for the total of these resultant forces.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of embodiment of the invention is clearly shown.

In the drawings:

Fig. 1 is a longitudinal sectional View taken through an axial piston pump or motor formed in accordance with the present invention.

Fig. 2' is a detailed sectional View taken on the Fig. 4 is a fragmentary detailed vertical sectional view taken through the connection between a piston and bearing shoe therefor andithe means for retaining the bearing shoe in engagement with the cam plate.

Fig. 5 is a vertical longitudinal, sectional view taken through a slightly modified form of the invention.

Fig. 6 is a detailed sectional view taken on the plane indicated by the line VIVI of Fig. 5.

Fig. '7 is a developed sectional view taken on the plane indicated by the line VII-VII of Fig. 6.

Fig.6 is a diagrammatic view showing the relation of the cylinder barrel, the pistons and the cam plate and'the forces acting thereon during the operation of the device.

Referring more particularly to the drawings, the numeral indicates generally the pump or motor shown in Fig. 1. This device includes a casing 2| having a body 22, a head 23, and an end cap 24. The body 22 is hollow to provide, in connection with the head and end cap, a chamber '25 within which the operating mechanism is disposed. The inner surface of the body 22 is formed with a cylindrical bearing surface 26 adjacent to the end engaged by the end cap 24. The function of this bearing surface will be set forth in the following description.

As illustrated in Fig. l, the head 23 has a pair of oppositely disposed ports 21 and 28, one of which constitutes the inlet while the other constitutes the outlet. These ports communicate at their inner ends with passages 30 and 3| extending to the chamber 25. The head 23 isalso provided with a central opening 32 through which the operating shaft 33 of the pump or motor projects into the chamber 25. At the outer end, the opening 32 is enlarged to receive an antifriction bearing 34 which rotatablysupports the shaft 33, a packing gland 35 being secured to the outer surface of the head 23 to prevent the escape of fluid around the shaft. The inner end of the shaft 33 is splined as at 36 and receives similar splines'formedin the central bore of a cylinder barrel 31, this connection serving to cause the rotation of the cylinder barrel when the shaft 33 is revolved. At one end, the cylinder barrel 3'! is provided with a bearing face 33 to which ports 49 extend from chambers 4i formed in the cylinder barrel. Between the face 38 and the inner surface of the head 23 there is disposed a valve plate '42, this member having sausage shaped ports 43 and 44 in open communication with the passages 38 and 3|, respectively. As the cylinder barrel revolves, the ports 40 therein will alternately register with the ports 43 and 44 to establish communication between the chambers 4| in the cylinder barrel and the inlet and outlet ports 21 and 28 in the head 23.

To yieldably urge the cylinder barrel 3! toward the plate 42 to prevent escape of fluidfrom the ports 43 and 44, the inner end of the shaft 33 is formed with a socket 45 and a tapped opening 43. The socket receives a bushing 41, the inner end of which has an internal flange for engagement by a coil spring 48. The outer end of this spring engages thehead of a screw 5| which is threaded into the hole 46 and applies compressive force to the spring. The force of this spring resulting from its tendency to expand serves to urge the bushing 41 further into the opening 45 and causes an annular flange 5|A atthe outer end of the bushing, to engage the outer end of the cylinder barrel and urge it toward the valve plate 42. This method of mounting the cylinder barrel serves to hold the bearing surface 38 in firm fluid sealing engagement with the meeting surface of {the valve plate 42, the latter being in turn held against the inner surface of the head 23. A pin 52 projects from the head 23 into the plate 42 to prevent the rotation of the plate 42 and insure communication between the passages 38 and 3| and the ports '43 and 44.

It will be noted that the opposite faces of the plate 42 are relieved at the inner and outer edges to reduce the areas of the sealing surfaces adjacent to the ports 43 and 44. This reduction in area serves to reduce the tendency of high pressure in either port to effect a separation between the head 23 and plate 42 and between the latter and the cylinder barrel. Since one of the ports 43 and 44 contains fluid at much higher pressure than the other port there is a strong tendency for the cylinder barrel to be tilted or tipped to one side, which if not counteracted will'cause uneven wear on the port plate 42 with consequent leakage and inefficiency.

To counteract this tendency, a particularbearing construction for the cylinder barrel has been provided. This bearing is secured by providing the cylinder barrel with a skirt-like flange 53 which projects from the cylinder barrel toward the end cap 24. The outer-surface of this flange is accurately finished and when the cylinder barrel is properly positioned will engage the cylindrical bearing surface 26 to support the cylinder barrel for rotation in the body 22. If desired, the flange 53 may be cast or otherwise formed integrally with the cylinder barrel or it may be formed from a separate piece of the same or a different material and pressed onto the cylinder'barrel depending upon the conditions under which the pump is to operate and the materials from which the parts are fabricated.

The chambers 4| in the cylinder barrel receive piston elements 54, the outer ends of which are formed with spherical heads 55. Bearing shoes 56 are connected with heads to provide for universal movement between these elements whereby the bearing surfaces of the shoes may constantly engage the bearing surface 510i a cam block 58 carried by the cap 24. The bearing surface 51 is inclined with respect to the axis of rotation of the cylinder barrel so that as the latter member revolves, the pistons 54 will be reciprocated in the cylinder barrel to draw in and expel fluid therefrom. To maintain the shoes '53 in sliding engagement with the surface 51 the shoes are formed with shoulders 60 for engagement by a retaining plate or disk Bl, the latter having openings 62 through which portions of the shoes 56 project for connection with the pistons. The openings 62 are larger in diameter than the portions of the shoes which they receive to permit relative lateral movement between these elements caused by the angular relation of the axes aboutwhich the pistons and the plate 6| revolve.

In the-formof the invention shown in'Figs. 1 to 4 inclusive, the retaining plate 6| has an opening at its central portion to receive a ball bearing assembly-63. This bearingassembly is pressed into the plate and "also secured tothe outer end of a stud 64 which by means of key 65, is guided for sliding movement in an opening formed in the block 58. The inner end of this opening is counterbored to receive a head 66 which is secured as shown in Fig. 4, by a screw 6'! to the inner end of the stud B4. A coil spring 68 has one end in engagement with the shoulder I formed by counterboring the opening while the other end engages the inner surface of the head 66. The force of this spring 68 serves to resiliently maintain the bearing shoes 56 in sliding engagement with the bearing surface 51 of the block 58.

As illustrated in Figs. 2 and 3, each bearing shoe 56 in one form of the invention has its cam plate-engaging portion shaped similarly to a sector-like portion of a ring, the shoes being of such size that when they are in assembled engagement with the cam plate, a limited degree of clearance will exist between adjacent edges of the shoes. As shown in Fig. 3 this close proximity of adjacent shoes serves to prevent the rotation of the shoes about'the point of connection thereof with the pistons and, therefore, eliminates wear caused by such action. It will also be noted from Figs. 2 and 3 that the surfaces of the shoes in engagement with the cam plate are provided with shallow, circular recesses ll which communicate by reduced passages 12, 13, and 14 formed in the shoes and pistons, respectively, with the chambers 4| in the cylinder barrel. Thus, when the cylinder barrel revolves and the chambers 4i communicate with the high pressure port, such pressure will be transmitted to the recesses H and will tend to force the shoes away from the cam plate.

By limiting the size of the'recesses and the area of the surfaces exposed to such fluid pressures, the tendency of the shoes to separate from the cam plate may be controlled; it being desirable to provide suflicient force to substantially counteract the force transmitted to the pistons by the fluid being pumped, but not enough force to cause the bearing shoes to separate or break contact with the cam plate. The area of the bearing surfaces of the shoes subject to the tendency of the fluid pressure to separate the shoes from the cam plate is limited by a ring-like groove 15 surrounding each recess II. The grooves 15 are vented to the interior of the chamber 25 by short grooves 16. This groove arrangement thus provides auxiliary bearing surfaces 11 on the shoes which surfaces are not exposed to the action of the separating pressure. It will be noted from Fig. 1 that the flange 53 on the cylindery...

barrel projects a slight distance beyond the point of engagement of the pistons and shoes, and the areas of contact of the shoes with the cam plate. In the operation of the pump, the tendency of the cylinder barrel to move laterally due to the inclination of the cam plate and the force transmitted to the latter by the pistons will be counteracted by the engagement of the flange 53 with the bearing surface 26.

The pump 18 shown in Fig. 5 is similar in construction and operation to that shown in Fig. 1. This pump 18 differs only in the method of maintaining the sliding engagement of the bearing shoes and the cam plate and in the manner in which rotation of the bearing shoes around their points of connection with the pistons is prevented. In this form of the invention the bearing shoes 88 have circular swash plate engaging portions 8| which are provided with recesses 82 corresponding in function and operation to the recesses H in the shoes 56 first described.

As shown in Fig.6, each bearing shoe has its edge portion notched atone side as at 83, to receive the adjacent circular edge portion of the next bearing shoe. This engagement of the bearing shoes prevents their relative rotation in the same manner as the engagement between hearing shoes 56 in the first form of the invention. It has been found through actual experience that circular bearing shoes which have a limited auxiliary bearing area are most desirable when certain. materials are used in the construction of the bearing shoe while the sector-shaped shoes in which a larger auxiliary bearing surface is provided, are desirable when other materials are used. To hold the bearing shoes in the second form of the invention in engagement with the swash plate the retaining plate 84 has a spherical socket 85 provided at its center of rotation. This spherical socket receives the ball shaped end of a plunger 86 which is slidably disposed in" a sleeve 81 corresponding to the sleeve 41 in the form of the invention first described. The sleeve 81 is disposed for longitudinal movement in a socket in theshaft 88 of the pump or motor.

With the parts so constructed and assembled a single spring 89 disposed between the. inner end wall of the sleeve 8'! and the inner end of the plunger 86 serves to urge the cylinder barrel toward the port plate and the retainingplate 84 toward the swash plate 90. Due to theball and socket connection between the plunger 86 and the retaining plate 84, the latter is free to revolve with the cylinder barrel during the operation of the pump or motor.

It will be observed from an inspection of Figs. 5 and 8 that the skirt-like flanges 53 and 9| on the cylinder barrels 31 and 92'project beyond the pointsof connection of the bearing shoes and pistons. It has been determined that during the operation of the pump, the pistons are subject to forces, represented by arrows Ain Fig; 8, tending to move the same out of the cylinderbarrel toward the cam plate. Also that these forces are counteracted by forces, indicated by arrows B in Fig. 8, transmitted by the cam plate to the pistons through the bearing shoes. These forces converge at the centers of the ball and socket joints between the pistons and bearing shoes and produce resultant forces, indicated in Fig. 8 by arrows C These resultant forces are directed laterally and are transmitted by the pistons to the cylinder barrel and tend to move this member in the same direction. The bearing surface 26 has been provided to resistthe movement-0f the cylinder barrel by this force thereby maintaining the desired sealing engagement between the cylinder barrel end surface and the port plate. V g

One of the features of the present invention is the locationof the bearing surface 26. As shown in Fig. 8, the points at which the forces C originate are spaced axially of thepump due to the inclination of the cam surface 51. The bearing surface 26 is therefore disposed symmetrically about a plane passing through the median point of the resultant forces. .Bearing 26oifersa resisting force, indicated by the arrow-D to the lateral movement of the cylinder barrelwhich force D, being applied in alignment with the resultant forces C, effectively prevents the tipping of the cylinder barrel.

While the form of embodiment of the present invention as herein disclosed constitutes a pre:

ferred form, it is to be understood that other forms mightbe adopted, all coming within the scope of the claims whichfollow.

What is claimed is:

1. In a fluid pressure energy translating device, a casing provided with a sleevelike bearing surface; a valve plate in said casing; a rotatable cylinder barrel in said casing, one end of said cylinder barrel abutting said valve plate; an inclined cam plate at one end of said cylinder barrel; a plurality of pistons disposed for movement in'said cylinder barrel; a bearing shoe having a universal connection with each piston and a sliding engagement with said cam plate; a retainer plate disposed in parallel relation to the face of said cam plate, said retainer plate engaging said bearing shoes; means engaging said retainer plate adjacent the central portion thereof to rotatably support said plate and urge the same toward said cam plate; and a skirt-like flange projecting from said cylinder barrel around said cam plate and bearing shoes, said flange having a bearing engagement with the sleeve-like bearing surface in said casing.

2. In a fluid pressure energy translating device, a casing having a cylindrical bearing surface; a valve plate in said casing; a cylinder barrel rot-atbly disposed in said casing with one end thereof engaging said valve plate; a plurality of pistons movably supported in said cylinder barrel; an inclined cam plate at one end of said cylinder barrel, said pistons having operative engagement.

with said cam plate whereby said pistons reciprocate in said cylinder barrel; and a continuous skirt-like flange projecting from said cylinder barrel beyond the points of engagement of said pistons and cam plate, said flange having a bearing engagement with the cylindrical bearing surface in said casing, the rest of the cylindrical surface of said cylinder barrel being spaced from said casing.

3. In a fluid pressure energy translating device, a member provided with an internal cylindrical bearing surface; a valve plate in said member; a cylinder barrel disposed within said member for rotary movement, one end of said cylinder barrel abutting said valve plate; a plurality of pistons movably supported in said cylinder barrel; an inclined cam plate at one end of said cylinder barrel; said pistons being operatively engaged with said cam plate whereby the pistons reciprocate in said cylinder barrel, the bearing surface in said member being symmetrical about a plane passing through the median point of the operative engagement of said pistons and said cam plate; and a continuous skirt-like flange on said cylinder barrel for engaging the cylindrical bearing in said member to support said cylinder barrel.

4. In a fluid pressure energy translating device, a member provided with an internal cylindrical bearing surface; a valve plate in said member; a cylinder barrel disposed within said member for rotary movement, one end of said cylinder barrel engaging said valve plate; a plurality of pistons movably supported in said cylinder bare rel; an inclined cam plate at one end of said cylinder barrel; bearing shoe means having ball and socket connection with said pistons, said shoe means being slideably engaged with said cam plate, the bearing surface in said member extending substantially equal distances on opposite sides of a plane disposed at right angles to the axis of rotation of said cylinder barrel and extending through the median point of the ball and socket connections between said pistons and bearing shoes; and a skirt-like flange provided on said cylinderbarrel for engagement with said cylindrical bearing surface to resist lateral movement of said cylinder barrel.

5. In a fluid pressure energy translating device, a rotatable cylinder barrel; an inclined cam plate on one end of said cylinder barrel; a plurality of pistons disposed for movement in said cylinder barrel; a circular bearing shoe universally connected to each piston and having a surface in engagement with said cam plate; and a recess on each shoe for receiving a portion of the next adjacent shoe to provide an interlocking relationship whereby relative rotation of the shoes is prevented.

6. In a fluid pressure energy translating device, a casing; a port plate in said casing at one end thereof; a cam plate in said casing at the opposite end thereof; bearing means in said casing intermediate the ends thereof; a cylinder barrel supported for rotation in said bearing means, one end of said cylinder barrel being in bearing engagement with said port plate; piston means movably mounted in said cylinder barrel; shouldered bearing shoe means universally connected with said piston means and engaging said cam plate; a retainer disk engaging the shoulders on said shoe means; and resiliently biased means between said cylinder barrel and said retainer plate tending to urge said cylinder barrel toward said port plate and said shoes toward said cam plate, said resiliently biased means having a universal connection with said retainer plate; the centers of said universal connections being spaced substantially equidistantly from the face of said cam plate, the connections between said pistons and shoes being movable during the rotation of said cylinder barrel through points spaced substantially equidistantly on opposite sides of a plane which substantially bisects the bearing means in said casing.

7. In a fluid pressure energy translating device, a casing; a port plate in said casing at one end thereof; a cam plate in said casing at the opposite end thereof; bearing means in said casing intermediate the ends thereof; a cylinder barrel supported for rotation in said bearing means, one end of said cylinder barrel being in bearing engagement with said port plate; piston means movably mounted in said cylinder barrel; bearing shoe means universaly connected with said piston means and engaging said cam plate; and resiliently biased means tending to urge said cylinder barrel toward said port plate and said shoes toward said cam plate, the centers of the universal connections between said pistons and bearing shoes bein spaced equidistantly from the face of said cam plate and moving during the rotation of said cylinder barrel equidistantly on either side of a plane extending normal to the axis of said device and substantially bisecting the bearing means in said casing.

8. In a fluid pressure energy translating device, a casing; a valve plate in said casing; a cylinder barrel havin one end abutting said valve plate; an inclined cam plate disposed adjacent the other end of said cylinder barrel, the latter being rotatable relative to said plates; piston means movably received by said cylinder barrel, said piston means having ball-shaped heads at the outer ends thereof; bearing shoe means disposed in sliding engagement with said cam plate, said bearing shoe means having spherical sockets for the ball-shaped heads of said pistons; means for maintaining the engagement of said shoe means with said cam plate, said means having a retainer plate and a yieldably pressed member; and a bearing in said casing for the end portion of the cylinder barrel adjacent said cam plate, said bearing extending a substantial distance beyond a plane disposed normal to the-axis of said cylinder barrel and passing through the median point of the ball and socket connections between said shoes and pistons, the bearing terminating in spaced relation from the end of said cylinder barrel adjacent said valve plate.

9. In a fluid pressure energy translating device, a casing having a cylindrical bearing surface; a valve plate in said casing; a cylinder barrel disposed for rotation in said casing with one end in engagement with said valve plate; piston means disposed formovement in the cylinders in said barrel; a skirt projecting from the end of said cylinder barrel and providing a recess, said skirt engaging said bearing to support said cylinder barrel; bearing shoe means universally connected to said piston means; and an inclined cam plate surface engagin said bearing shoe means to impart reciprocatory movement to said pistons, said bearing shoe means and said cam plate surface being disposed in the recess formed by said cylinder barrel skirt.

10. In a fluid pressure energy translating device, a casing; a rotatable cylinder barrel; a valve plate in engagement with one end of said cylinder barrel; pistons disposed for reciprocation in said cylinder barrel; a cam plate positioned at one end of said cylinder barrel to impart reciprocatory movement to said pistons, the action of said cam on said pistons and the resistance offered by the fiuid causing a resultant lateral force on each piston, such forces being transmitted to said cylinder barrel; and radial bearing means engaging said cylinder barrel and said casing for rotatably supporting said cylinder barrel and resistin lateral movement thereof by said resultant forces, said bearing means being disposed substantially symmetrically about a plane normal to the axis of rotation of said cylinder barrel and extending parallel with said resultant forces and passing through the median point of origin thereof.

11. In a fluid pressure energy translating device, a casing providing a chamber; a shaft journalled for rotation in said casing and projecting into said chamber; a valve plate supported by said casing within said chamber; a cylinder barrel having a sliding engagement with said valv plate and a drivin connection with said shaft; pistons disposed for reciprocation in said cylinder barrel; a cam plate positioned in said chamber to impart reciprocatory movement to said pistons, the action of said cam on said pistons and the resistance offered by the fluid causing a resultant lateral force on each piston, such forces being transmitted to said cylinder barrel; and radial bearing means disposed in said casing and engaging said cylinder barrel for rotatably supporting the same and resisting lateral movement thereof by said resultant forces, said bearing means projecting on either side of a plane normal to the axis of rotation of said cylinder barrel and extending parallel with said resultant forces and passing through the median point of origin thereof.

12. In a fluid pressure energy translating device, a casing providing a chamber; bearing means in said casing; a shaft supported for rotation in said bearing means, said shaft projecting into said chamber; a valve plate supported by said casing within said chamber; a cylinder barrel disposed in said chamber in sliding engagement with said valve plate, said cylinder barrel having a driving connection with said shaft; pistons disposed for reciprocation in said cylinder barrel; a cam plate in said chamber for controlling the reciprocatory movement of said pistons; bearing shoe means universally connected with said pistons and engaging said cam plate; and a radial bearing mounted in said casing and engaging said cylinder barrel for rotatably supporting the same, said radial bearing extending on either side of a plane disposed normal to the axis of rotation of said shaft and passin through the median point of connection of the pistons and bearing shoes.

13. In a fluid pressure energy translating device, a casing providing a chamber; bearing means in said casing; a shaft supported for rotation in said bearing means, said shaft projecting into said chamber; a valve plate supported by said casing within said chamber; a cylinder barrel disposed in said chamber in sliding engagement with said valve plate said cylinder barrel having a driving connection with said shaft; pistons disposed for reciprocation in said cylinder barrel; a cam plate in said chamber for controlling the reciprocatory movement of said pistons; bearing shoe means universally connected with said pistons and engaging said cam plate; a retainer plate in engagement with said bearing shoes; a yieldably pressed member universally engaged with said retainer plate and operative to urge the plate and bearing shoes toward said cam plate, said yieldably pressed member being arranged on the axis of rotation of said shaft, the centers of the universal connections between said member and retainer plate and between said bearing shoes and pistons being disposed in a plane extending parallel to said cam plate; and a radial bearing rotatably supporting said cylinder barrel, said radial bearing extending a limited distance on either side of a plane disposed normal to the axis of rotation of said shaft and passing through the center of the universal connection between said yieldably pressed element and said retainer plate.

ELLIS H. BORN REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,632,304 Maurer June 14, 1927 1,710,567 Carey Apr. 23, 1929 1,772,828 Egersdorfer Aug. 12, 1930 1,945,391 Benedek Jan. 30, 1934 1,952,994 Laird Mar. 27, 1934 2,016,082 Elrod Oct. 1, 1935 2,081,477 Egersdorfer May 25, 1937 2,168,658 Thomas Aug. 8, 939 2,299,234 Snader et al Oct. 20, 1942 2,300,009 Rose Oct. 27, 1942 2,331,694 Jeffrey Oct. 12, 1943 FOREIGN PATENTS Number Country Date 235,452 Great Britain June 18, 1925 311,938 Great Britain 1929 597,476 Germany Apr. 26, 1932 754,179 France Aug. 21, 1933 

